1. Technical Field
The present disclosure relates generally to regenerative heat exchangers and, more particularly, to a rotary heat exchange wheel for transferring heat between two counter-flowing air streams. Even more particularly, the present disclosure relates to a regenerator matrix of a rotary heat exchange wheel having wound layers of smooth film spaced apart with a combination of dimples and elongated embossments.
2. Related Art
Regenerator heat exchange devices or regenerators are well known for effecting the transfer of heat and moisture between two counter-flowing air streams. Such heat exchange devices are used, for example, in heating, ventilation and cooling (HVAC) systems to conserve energy within buildings. One type of regenerator is the rotary air-to-air heat exchanger, which is typically in the form of a rotary heat exchange wheel including a matrix of heat exchange material. When rotated through counter-flowing air streams, the rotating wheel matrix is heated by the air stream with the higher temperature and, in turn, heats the lower temperature air stream. In addition, the rotating wheel may transfer moisture between the counter-flowing air streams. To promote moisture transfer, the wheel heat exchange matrix can be made from, or coated with, a moisture adsorbent desiccant material.
A matrix of a rotary heat exchange wheel can include strips of thin film material wound about an axis of the wheel so as to provide a plurality of layers. In such a design, the layers must have spacing means to create gas passageways extending through the wheel parallel with the axis. The layers must be uniformly spaced apart so that the gas passageways are of uniform height throughout their length for greatest efficiency.
Transverse elongated embossments have been provided in a plastic strip to form the gas passageways between the layers of the regenerator matrix. Numerous closely spaced transverse embossments are needed to maintain parallelism between layers if used alone to form the passageways. While such elongated embossments may maintain parallelism and prevent circumferential gas leakage, they replace parallel matrix surface area thereby reducing the heat exchange effectiveness of the regenerator.
For optimum heat and moisture transfer and from a manufacturing standpoint, it is easiest to merely provide dimples in the strip to form the gas passageways between the layers of the regenerator matrix. However, while dimples provide a desirable high aspect ratio between layers, they unfortunately allow appreciable circumferential gas leakage in those situations where there is a high pressure differential between the counter-flowing air streams, thereby reducing the heat exchange effectiveness of the regenerator.
Canadian Patent No. 1,200,237, which issued on Feb. 4, 1986 and is assigned to the assignee of the present disclosure, provides a regenerator matrix for use as a counter-flow heat regenerator. The matrix includes a wheel of plastic film strip material formed about a center axis of the wheel so as to provide a plurality of layers of the film material. At least some of the layers include elongated embossments extending substantially parallel to the axis of the wheel, with alternate embossments protruding from opposite surfaces of the strip material.
The transverse embossments provide spaces between layers of the film material and define passageways for gas passing through the matrix parallel to the center axis. The embossments have a total length less than the width of the strip and do not extend to the edges of the strip, but do manage to resist most circumferential gas leakage around the wheel. However, because the embossments do not extend to the edges of the strip they have closed ends that reduce the traverse area of the passageways. In one of the embodiments shown, the elongated embossments are discontinuous, while in another embodiment dimples are provided between the elongated embossments to maintain uniform spacing of the layers.
What is still desired is a new and improved regenerator matrix for a rotary heat exchange wheel that provides substantially no circumferential gas leakage-within the matrix, while still having a high heat exchange effectiveness.